The monarch defense: In chess and in life

Emory evolutionary biologist Jaap de Roode has had some strange assignments in his academic career. In his early days as a researcher, for example, his job was to measure the penis size of Malaysian dung beetles.

So it was no big deal when a photographer for Popular Science magazine asked de Roode to pose at a chessboard, pretending to watch two opponents: A butterfly and a bio-hazard bottle that was standing in for a parasite. The photo shoot was to illustrate the Popular Science “Brilliant 10,” top scientists under 40 from across the nation recognized by the editors of the magazine.

De Roode was declared “Brilliant” for his discovery of how monarch butterflies treat themselves and their offspring for parasites, using medicinal plants.

“I liked the concept of the chess game,” says de Roode. “That really is how scientists view the co-evolutionary process of a host and its parasites. One makes a move, and the other responds with a defense or attack.”

Many scientists have argued that animal medication requires great cognitive ability, memory and learning behaviors, and that self-medication may be restricted to a handful of animals, such as chimpanzees and gorillas. Research by the de Roode lab, however, clearly shows that very simple and small-brained animals can use “natural” medicine.

De Roode’s findings, which were published in Ecology Letters, suggest that animal medication is probably much more widespread than originally thought, opening the door for many new discoveries of medication in nature.

Currently, de Roode is studying different populations of monarchs, to determine whether they use medication only therapeutically, when they are already infected with parasites, or as a preventative, when they live in areas with a higher risk of infection.

He explains the hypothesis with a human analogy: “If we travel to Africa, we may take anti-malaria drugs prophylactically, but while we’re at home in the United States we don’t use them. You don’t want to take drugs when you don’t need them.”

In previous work, de Roode provided a new perspective on another long-standing question in evolutionary ecology: How do parasites strike the balance between living off of their hosts and killing them?

A prevalent theory – still proclaimed by most medical doctors – was that over time, parasites become less virulent and evolve a capacity to be nearly harmless to their hosts.

De Roode’s work revealed a different underlying strategy, showing that instead of becoming kinder, parasites may actually be selected to be virulent and deadly. By doing so, they produce more offspring, which increases the chances of the parasite jumping to new hosts.

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The monarch butterfly's medicine kit